I am not a lawyer either but "ignorance of the law is not a defense" and as a person interested in engaging in creative activities I've made an effort to understand the law so I know generally where the boundaries are. As far as I can tell @hivewatchers tends to flag content used that isn't credited in some way.

I live in California which makes me a United States citizen. United States Code Title 17, section 107 allows limited use of copyrighted materials without prior permission. This is known as the "fair use" doctrine. Also, as a California citizen I am within the Ninth Circuit court which historically has been one of the most favorable Appeals Courts toward claims of fair use.

I consciously strive to abide by U.S. copyright law. When I need to use content I don't own my first search is through public domain or Creative Commons. If that fails I'll see if anything similar to what I need is available as an embedded link such as a YouTube video. If all else fails and I need to upload a copy I credit the source. I don't just upload other people's content for giggles or a quick buck. It's for the purposes of commentary and/or analysis as the law allows.